Immunocytochemical study of the cellular immune response in meningiomas.

Twenty four meningiomas (17 benign and seven "atypical" were reacted with a panel of monoclonal antibodies to macrophages, lymphocytes, and HLA DR antigens. All the tumours contained macrophages but these cells were more numerous in the atypical meningiomas. Lymphocytes, almost exclusively of the CD8 subtype, were also present in 70% of benign meningiomas and in all atypical meningiomas and were more abundant in the latter. B lymphocytes were present in minimal numbers in three atypical meningiomas and in one benign meningioma. CD4 positive T lymphocytes were present in small numbers in one benign meningioma and in moderate numbers in one atypical meningioma. HLA DR antigen expression on tumour cells was present in about 60% of both tumour groups. The numbers of macrophages and T and CD8 lymphocytes in meningiomas seem to be related to atypical histological features, and the presence of these cells raises questions about host immune response and the relation of this to prognosis.